Well.. Basically anything in the "obscure" category. Most genres/subgenres consist of dark ambient, black metal (raw, symphonic, suicidal), death metal (brutal, gore, depressive), doom (funeral), and anything inbetween. Anything that reflects extreme negative/angry/depressive emotions/messages. The music in which the band creates is usually either ugly or beautiful, in its own unique way. What throws most people off is the vocals, because they are so out of this world, and unusual. To me its a perfect compliment to the music. Before spending your money its best to ask a fan if its any good though first, so keep that in mind. Sometimes some of the genres can be slightly repeditive, but I think it adds to the atmosphere because its often hypnotic. As far as certain titles to look for it wont be easy because most of the bands in those genres are "underground", which means their music is extremely hard to come by pretty much unless you luckily find it on ebay or something. Ill start you off easy though, and say Burzum. Mr. Vikernes's material usually isnt that hard to come by The song "Det Som En Gang Var" (not the album) put me in a profound trance the first time I heard it. (I also played it at work once and someone said "this music makes me want to kill myself"). The song Dunkelheit from Filosophem by him is another useful one. Hope this helps. And by the way, his album ASKE/Burzum is generic and nothing special in my opinion, he has these two ambient albums as well which are quite good though. On Dauði Baldrs for example, the last two tracks are beautifully depressive, and on Hliðskjálf the song Der Tod Wuotans is the most depressing one Id say.